The present invention relates to a method for conditioning a mixture of particles with a surface active reagent and to apparatus for performing the method of this invention. More particularly, this invention relates to a method for selectively wetting surface areas of particles which are receptive to coating by a preselected wetting agent or surface active reagent.
Selective wetting of particles is required for many operations for separating a mixture of particles. In particular, the selective wetting of particles is practiced in the mining and ore beneficiating art for separating minerals from the ore in which it is contained. Some methods used to separate a mineral from the other components within a mineral ore rely on the differences in the surface chemical properties of the components in the ore. The surface chemical properties of a particle of ore depend upon components present in that particle of ore. As the particles contain varying compositions, desired particles can be distinguished and thereby separated from undesired particles according to their composition, through use of the surface chemical properties of the individual particles.
In order to make use of the differences in the surface chemical properties of the particles of ore, it is often necessary to contact the mixture of particles with a surface active reagent that will selectively react with some surface portions of the particles due to the selectivity of the reagent in distinguishing between surface chemical properties. The term "react" within the context of the present invention is meant to be a chemical reaction, a physical reaction, or a combination thereof as applicable to the surface areas of particles under consideration herein.
The process of contacting a mixture of particles with a surface active reagent is referred to in the art as "conditioning." Methods of particle separation in which it is necessary to condition the particles include methods such a flotation separation and optical separation. In flotation separation the particles to be separated are conditioned with a flotation agent. However, this process is typically limited to small particles which can be "floated" in a medium. A major disadvantage in this process is the cost and energy required to reduce the ore to a suitable size for flotation.
In a fluorescent, or optical separation method, the mixture of the particles to be separated may be conditioned with an aqueous dispersion of a suitable surface-active reagent and a fluorescent material (e.g. a dye). The coated surface areas on the particles exhibit fluorescence when exposed to electromagnetic radiation, such as ultraviolet light. Particles poorly coated with the surface active reagent do not exhibit significant fluorescence when exposed to electromagnetic radiation and hence are distinguishable from particles having larger coated surface areas. Based on the difference in fluorescence, coated particles can be effectively separated from those which are poorly coated in a machine as designated in Mathews U.S. Pat. No. 3,472,375; U.S. Pat. No. 3,356,211; U.S. Pat. No. 3,722,676 (all of which are incorporated herein).
The methods currently employed for conditioning particles generally consist of either one of two conditioning methods. One current method practiced includes submerging the mixture of particles to be separated in a fluid bed containing the surface active reagent. A disadvantage of such a method is that a large reservoir of the surface-active reagent is necessary to continuously wet the mixture of particles as the particles move through the fluid bed. Another disadvantage of such a method is that all surface portions of the particles receptive to the surface-active reagent may not be coated because of contact of the particle with the transfer device which conveys the particle through the fluid bed. This partial coating of the particle may inhibit the efficient separation of the particles from the mixture because all surface areas receptive to coating should be coated to effect efficient later separation of the particles.
A second method of wetting a mixture of particles includes spraying the surface active reagent onto the mixture of particles as the particles move on a conveyor belt or a vibrating screen. In this method, however, the particles also may not have all the surface portions thereon receptive to the surface-active reagent coated because of particle contact with the belt. Even if the belt were vibrating some surfaces receptive to surface-active reagent may not be coated by the reagent. As the particles are also in contact with a surface, there may also be smearing of the surface-active reagent on the particle and on the particles that are not normally surface chemically active with the reagent.